The present invention relates to methods of making a plurality of agglomerate abrasive grains and abrasive articles. More particularly, the present invention relates to spray-drying methods of making a plurality of agglomerate abrasive grains and abrasive articles.
Various agglomerate abrasive grains are known in the art and have been used in a variety of abrasive articles such as coated abrasive articles (see, e.g., U.S. Pat. No. 3,916,584 (Howard, et al.); U.S. Pat. No. 5,714,259 (Holmes, et al.); U.S. Pat. No. 4,311,489 (Kressnar); U.S. Pat. No. 4,652,275 (Bloecher, et al.); U.S. Pat. No. 4,799,939 (Bloecher, et al.); U.S. Pat. No. 5,500,273 (Holmes, et al.); and U.S. Pat. No. 5,910,471 (Christianson, et al.)). Some of the known methods for making agglomerate abrasive grains can be disadvantageous because of their inability to provide a plurality of extremely small (e.g., diameters of 500 micrometers or less), spherical agglomerate abrasive grains.
A problem encountered with some known methods of making polymer (e.g., organic resin) bonded agglomerate abrasive grains is such agglomerate abrasive grains are not as strong as desired.
Yet, another problem is that some techniques for making of agglomerate abrasive grains require heating to temperatures on the order of 1200xc2x0 C. to 1600xc2x0 C. Certain agglomerate abrasive grains (e.g., diamond and cubic boron nitride abrasive grains) are not stable at such temperatures.
The present invention provides a spray drying method for making a plurality of agglomerate abrasive grains. The method comprises:
spray drying slurry to provide a plurality of precursor agglomerate abrasive grains, the slurry comprising:
first mineral particles having a Moh""s hardness of at least about 5;
glass frit;
solvent; and
at least one of solvent-dispersible binder material or solvent-soluble binder material;
heating the plurality of precursor agglomerate abrasive grains to at least one temperature such that the glass frit at least partially fuses to provide a plurality of agglomerate abrasive grains each comprised of the first mineral particles bonded together via glass binder material.
In a preferred method according to the present invention, at least a portion (preferably, at least a majority by weight) of the first mineral particles having a Moh""s hardness of at least about 5 are at least one of diamond abrasive grains or cubic boron nitride abrasive grains. This method can be used to make agglomerate abrasive grains comprised of at least one of diamond abrasive grains or cubic boron nitride abrasive grains at temperatures substantially below the temperatures at which diamond and/or cubic boron nitride is thermally unstable.
In another preferred method according to the present invention, the resulting agglomerate abrasive grains can be made having a fine grade (i.e., a small particle size). Typically the agglomerate abrasive grains made according to the method of present invention have an average particle size ranging from about 1 micrometer to about 500 micrometers, more typically about 1 to about 300 micrometers, even more typically about 1 to about 250 micrometers, and most typically about 1 micrometer to about 200 micrometers.
Agglomerate abrasive grains made according to the present invention may be incorporated into various abrasive articles such as coated abrasives, bonded abrasives (including vitrified and resinoid grinding wheels), nonwoven abrasives, and abrasive brushes. The abrasive articles typically comprise agglomerate abrasive grains made according to the present invention and abrasive article binder material. As one non-limiting example, at least a portion of the plurality of agglomerate abrasive grains can be combined with abrasive article binder material to provide an abrasive article. In one such embodiment, the method further comprises heat-treating the glass binder material to provide ceramic binder material bonding the first mineral particles together prior to combining at least a portion of the plurality of agglomerate abrasive grains with abrasive article binder material. As another non-limiting example, an abrasive layer comprising at least a portion of the plurality of agglomerate abrasive grains dispersed within abrasive article binder material is applied to a major surface of a backing to provide a coated abrasive article. In one such embodiment the method further comprises heat-treating the glass binder material to provide ceramic binder material bonding the first mineral particles together prior to applying the abrasive layer comprising at least a portion of the plurality of agglomerate abrasive grains dispersed within abrasive article binder material to the major surface of the backing to provide the coated abrasive article. It is also within the scope of the invention to heat-treat glass binder material to provide ceramic binder material after making an abrasive article (e.g., when the abrasive article binder material is a glass or crystalline ceramic).
Some preferred, agglomerate abrasive grains made according to the present invention are sufficiently porous to allow the abrasive article binder material to penetrate therein, which in some applications (including some coated and bonded abrasive articles) may be advantageous. In another aspect, embodiments of agglomerate abrasive grains made according to the present invention may be made having a desired level of porosity and/or bond strength between the mineral particles in order to provide preferential wearing of the agglomerate abrasive grains. Such preferential wearing of the agglomerate abrasive grains may be particularly desirable for bonded abrasive articles.
Alternatively, for example, the agglomerate abrasive grains made according to the present invention may be used as in loose form, including in abrasive slurries and as shot blast media.
As used herein, the terms xe2x80x9cplurality of agglomerate abrasive grainsxe2x80x9d and xe2x80x9cagglomerate abrasive grainsxe2x80x9d are considered to be synonymous.